Neodymium-doped glass and neodymium-doped yttrium aluminum garnet single crystals (YAG) are commonly used as laser materials. The invention relates to the co-precipitation of a ceramic to be used as a solid laser material having an emission line width between that of neodymium-doped glass and YAG. Such a material is suitable for generating high average power combined with high peak power.
Neodymium-doped yttrium oxide ceramic is attractive as a laser material because it is expected to yield a higher energy output than either Nd-doped YAG or glass. The use of Nd.sup..sup.+3 as a fluorescent center in laser hosts has a principal advantage of providing a low threshold of stimulated emission at 1.078.mu. and places a premium on optical homogeneity and a low cavity loss. Numerous glass compositions and the crystal YAG are currently the most important host materials utilizing Nd.sup..sup.+3 fluorescence for laser action. Glass can be made in larger sizes with excellent optical homogeneity, and being amorphous, has the inherent properties of high energy storage capability (low gain) and low thermal conductivity. On the other hand, YAG crystals are expensive and limited in size by crystal growth considerations. They have a relatively high thermal conductivity and a low energy storage capability (high gain). For these reasons, glass is favored for high energy Q-switched pulses while YAG is best suited to C.W. applications. Using the conventional rod design, high average pulsed power cannot be produced with either host. Yttrium oxide ceramic, whose properties are intermediate between those of glass and YAG. has the potential for achieving a higher average pulsed power than either glass or YAG.
To be useful, though, as a laser material, it is best if the ceramic is pore free, transparent, free of light scattering inclusions and chemically homogeneous. Currently, however, processing of neodymium-doped yttrium ceramic materials may result in a product having occasional pores or other inhomogeneities.
Similarly, precipitation of yttrium oxide powder to produce laser material often results in a ceramic suffering from "orange peeling". Orange peeling is an optical undulation in the structure due to a refractive index variation. Its cause is not known. Standard techniques for the reaction of a Y -- Th -- Nd salt solution with oxalic acid to form the neodymium-doped yttrium oxide powder often result in a ceramic having orange peel.